Signs are very important for everyone. There are a lot of signs around the world. You can find warning（警示）signs and direction（方向）signs everywhere.
A warning sign tells us not to do something. "No smoking" is a warning sign. It means we mustn't smoke. We can see it in the museums, cinemas or theaters. A direction sign tells us how to get to a place, for example, the sign 
means we can turn right.
There are also some signs in the nature. We can tell the direction from the sun in the sky. The sun rises in the east, and goes down in the west. When the first green leaf comes out, it's the sign of spring. When the leaves turn yellow, it's the sign of autumn.
Now we can tell the weather from the weather forecast（天气预报）on TV. But people in the past told the weather from the clouds in the sky. Red clouds in the morning mean bad weather. Red clouds in the evening mean the weather will be fine tomorrow. So there is a famous Chinese old saying（谚语）：Red sky in the morning, sailors take warning. Red sky at night, sailors delight.
